1. Field of the Invention
The present invention relates to ultra-hard composite materials, and in particular relates to compositions of binder metals thereof.
2. Description of the Related Art
Since early 1920, ultra-hard composite materials have been widely applied in industry due to excellent properties such as high hardness, high thermal resistance, and high grinding resistance. One type of composite material, carbide, is popularly used and roughly divided into two types: tungsten carbide (hereinafter WC) based composite materials and titanium carbide (hereinafter TiC) based composite materials. The ultra-hard composite materials are composed of two different compositions. The first composition is ceramic phase powder with high melting point, high hardness, and high brittleness, such as carbide (tungsten carbide, titanium carbide, vanadium carbide, niobium carbide, chromium carbide, or tantalum carbide), carbonitride, borate, boride, or oxide. The second composition is binder metal with low hardness and high toughness. For example, the major binder metal for WC based composite material is cobalt. Alternatively, the major binder metal for TiC based composite material is nickel or nickel-molybdenum alloy. The method for manufacturing the ultra-hard composite materials is powder metallurgy. The binder metal transforms to a liquid state and further forms an eutectic liquid phase with the carbide under sintering temperature. Furthermore, the carbide powder is wrapped, cohered, and contracted by capillary motion to achieve high sintering density. For enhancing the sintering density, the ultra-hard composite materials are further processed by press sintering or hot isostatic pressing, such that advantages such as high hardness and high grinding resistance of the carbide and toughness of the binder metal are combined in ultra-hard composite materials.
The described ultra-hard composite materials are generally utilized in cutters, molds, tools, and grinding resistant device, such as turning tools, mills, reamers, planar tools, saws, drills, punches, shearing molds, shaping mold, drawing molds, extruding mold, watch sections, or the ball of pens. The WC ultra-hard composite material is most widely applied. The component ratio of the composite material is defined by requirement. Although a lower binder metal ratio combined with a higher carbide ratio produces a composite material having higher hardness and grinding resistance, it also causes the composite material to have lower toughness and higher brightness. If hardness and grinding resistance is mostly required, the carbide ratio should be enhanced. If toughness is more important, the carbide ratio should be reduced. In addition, if the device is used in corrosive conditions or high temperatures, the device should be anti-corrosive and anti-oxidative. The different requirements have been driven by the advancement of society, such that current production trends include higher yields, longer operating lifespan, and lower product costs of products such as cutters, molds, tools, and grinding resistant devices. Nonetheless, the toughness, thermal resistance, grinding resistance, anti-corrosiveness, and anti-adherence for traditional WC and TiC carbide ultra-hard composite materials are usually deficient when applied to different applications.
The binder metal of the traditional WC ultra-composite material is a cobalt based alloy with few amounts of iron and nickel. In Japan patent No. 8,319,532, the punch material is a WC based composite with binder metal (5-15 wt %) of a nickel based alloy. The nickel based alloy also includes 1-13 wt % Cr3C2. In Japan patent No. 10,110,235, the binder metal of the WC composite material is an iron based alloy, and the alloy further includes vanadium, chromium, vanadium carbide, and chromium carbide. In U.S. Pat. No. 6,030,912, the metal binder of WC and W2C composite material is 0.02-0.1 wt % metal such as iron, cobalt, nickel, and the likes and 0.3-3 wt % carbide, nitride, and carbonitride of transition metal of IVA, VA, and VIA groups. In U.S. Pat. No. 6,241,799, the sintering metal of WC is cobalt and/or nickel. In the binder metal formula, the cobalt is 90 wt % at most, the nickel is 90 wt % at most, the chromiun is 3-15 wt % at most, the tungsten is 30 wt % at most, and molybdenum is 15 wt % at most, restricting the WC crystal growth during sintering.
Presently, China is the largest consumer of WC ultra-hard composite materials. Therefore, a large number of WC ultra-hard composite material patents have been disclosed in China improving properties such as strength, hardness, toughness, and grinding resistance. In China Pat. No. CN 1,548,567, high-manganese steel serves as the binder metal of a WC composite. The high-manganese steel is composed of 14-18 wt % manganese, 3-6 wt % nickel, 0.19-1.9 wt % carbon, and 74.1-82.1 wt % iron. This WC composite has high strength, high hardness, and high grinding resistance. In addition, carbide may serve as part of the binder metal. In China Pat. No. 1,554,789, the binder metal includes 4-6 wt % cobalt and 0.3-0.6 wt % tantalum. The binder metal is sintered with a WC powder to form a WC composite material with higher grinding resistance and higher toughness. Furthermore, in China Pat. No. 1,718,813, the binder metal includes 7-9 wt % of cobalt, 0.1-0.5 wt % vanadium carbide, and 0.3-0.7 wt % of chromium carbide. The binder metal is sintered with a WC powder to form a WC composite material with high strength, high hardness, and high toughness.
Accordingly, the conventional metal binder has one metal or a combination of two metals as a major part (>50 wt %) doped with other metal elements and a carbide ceramic phase. However, the binder metal of the invention is a high-entropy alloy disclosed in Taiwan Pat. No. 193729. For the invention, the multi-element high-entropy alloy powder consists of five to eleven principal elements, with every principal element occupying a 5 to 35 molar percentage of the multi-element high-entropy alloy powder. The concept and effect of the multi-element high-entropy alloy is disclosed in Advanced Engineering Materials, 6, 299-303 (2004) by one inventor of the invention, Yeh. The paper discloses a high-entropy alloy composed of at least five principal elements, with every principal element occupying a 5 to 35 molar percentage of the high-entropy alloy. The binder metal composed of high-entropy alloy shows characteristics such as high-entropy effect, sluggish effect, lattice distortion effect, and cocktail effect, and has thermal resistance and hardness, such that the composite utilizing the binder metal has high hardness, high thermal resistance, and high grinding resistance. Additionally, because the sluggish effect of the high-entropy alloy makes the sintered binder metal during the liquid phase difficult to be transferred or diffused and prevents crystal growth of WC or TiC, hardness, toughness, thermal resistance, and grinding resistance of the sintered composite are not reduced. Moreover, because part of the elements in the binder metal combines with carbon to form carbides, hardness of the composite is increased. For the invention, nickel and chromium in the binder metal enhances anti-corrosive properties of the composite, chromium, aluminum, and silicon in the binder metal increases anti-oxidation, and copper in the binder metal increases lubricity of the composite. For the invention, the composite performance and operating lifespan can be adjusted by appropriate molar ratio and element type. Compared to the invention, the conventional binder metal is composed of fewer elements with less variation, thereby limiting the performance of the composite material.